Multinodular goiter of the thyroid mimicking malignancy: diagnostic pitfalls in fine-needle aspiration biopsy.

A case of multinodular goiter with multicentric papillary hyperplasia is presented with cytologic features suggestive of thyroid papillary carcinoma. While the cytologic criteria for papillary thyroid carcinoma is well defined, occasional diagnostic difficulties can arise. Cytologically, the presence of focal papillary aggregates, the presence of a psammoma body within a background of copious colloid and scattered follicular cells led to diagnostic confusion. Histologically, the presence of secondary follicles in the papillae and protrusion of the papillary structures into colloid lakes supported the diagnosis of goiter. It is our opinion that most, if not all, of these difficulties can be circumvented by the incorporation of all major and some minor cytologic criteria for papillary carcinoma in the analysis of such lesions. Single criteria for papillary carcinoma, either major or minor, is not sufficient.